In some wireless communication systems, such as, for example, the Long Term Evolution (LTE) system, the physical channels are shared among a plurality of users. Examples of shared channels in the LTE system are the Physical Downlink Shared Channel (PDSCH) and the Physical Uplink Shared Channel (PUSCH). Fast scheduling is used to ensure efficient resource usage. A scheduler at the base station schedules users and assigns resources on the shared channel based on factors such as the amount of data to be transmitted, quality of service (QoS) requirements, and instantaneous channel conditions.
To facilitate scheduling on the PDSCH, user terminals send channel quality indication (CQI) reports to the base station. The CQI reports indicate the instantaneous channel conditions as seen by the receiver at the user terminals. The base station uses the CQI reports to determine which user terminals to schedule to receive downlink transmissions in a particular scheduling interval. The base station also uses the CQI reports to select the modulation and coding scheme (MCS) and transport block size (TBS) for the downlink transmissions to a user terminal.
The implementation of CQI reporting is not defined in the LTE standard and is therefore dependent on vendor implementation. It has been observed that some variation exists in the CQIs reported by different user terminals under similar conditions. Some vendors may choose to configure user terminals to report CQI values higher than the actual CQI so that the scheduler at the base station will assign a higher TBS to the user terminal and thus obtain higher throughput for that user terminal. However, reporting CQI values higher than actual CQI will result in higher retransmission rates and lower system throughput. Similarly, non-calibrated handsets, i.e., rogue handsets, may also report CQI values higher than actual CQI with the same result.